iMac 2009 27" internal display black/blank but external working

I have an iMac End 2009 W8*****5RU. Recently while upgrading the HDD I had to unplug the LG built in display and while doing so the Vsync cable snapped. I put a new cable but now the internal display is detected but I don't see any image (completely dark black / blank screen, with no image even when I checked through torch light). The external display is working fine and iMac runs perfectly. I am wondering if I have the change the entire LCD panel or the inverter board? The Internal display connector (LVD) is slightly loose from the logic board but the pins are connected properly. I don’t see the 4th diagnostic LED turned on. How should I solve this issue to get back my internal display to work?

FYI: the display had fallen off while assembling and also the previous VSYNC flex cable (thin cable which connects to the inverter) was burnt.

Should I buy a new LCD panel or change the logic board/LED backlit inverter?

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